Automatic telephone system



a K ,62 @fi3 4 Apnl 26, 1927- E, ARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 2. 1921 4 Sheets-Sheet 1 Jbhn E-Earunar April 26, m7.

J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 2. 2 4 Sheets-SQ;

InUEn UI" wwdv wk 6201111 EEarUfisr rifi 26 1927, AP J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed 2. 1921 4 Sheets-Sheet 3 Zm E. Esrzfrzaf April 26, 1927. LfiZfiflBQ J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 2. 1921 4 Sheets-Sheet 4 Patented Apr. 26, 1927.

UNITED STATES PATENT JOHN E. GARDNER, or CHICAGO, rumors, lessrenon, BY MESNE assremurs, r auromrrc nnnc'rnro me, or cnroaeo, rrnmors A coaroaa'rron or DELA- WARE.

.AUTOMATIC TELEPHONE SYSTEM.

Application filed February 2, 1921, Serial No. 441,875. Renewed September 17, 1928.

The present invention relates in general to automatic telephone systems, but is more particularly concerned with systems of the t pe usually installed in small automatic ex- 5 c anges, such systems being commonly known as private automatic exchanges. Exchanges of this character are largely in. use in manufacturing or mercantile establishments of various kinds for providing local service be- 'm tween the different departments. The service requirements of such a system ar different from those in a public autom tic exchange and it is often necessary to provlde many features which are not generally used I in a larger system. The present invention is concerned particularly with one of these features, a scheme that is known as conference calling. This is an arrangement whereby three or more telephone hnesln a private automatic exchange may be telephomcally connected together at the same tlme.

The present invention contemplates a novel and improved means of effecting the above result, together with other features which will fully appear hereinafter. In order to simplify the description the invention has been shown applied to an isolated private automatic exchange, but it will be readily apparent that it is not limited to this use.

The drawings accompanying th s specification and comprising Figs. 1 to ft, inclusive, show by means of the usual circuit diagrams suflicient of the apparatus in a private automatic exchange to enable the invention to be explained and understood. Figure 1 shows two automatic substations -A and A, with their associated individual line switches C and C; Figs. 2 and 4 show two automatic connector switches which are accessible to the subscribers individual line switches, and

which in turn have access to the subscribers" lines; while Fig. 3 shows a special rotary line switch which has access to the connector switches in common with the subscribers individual line switches, and which is accessible to the connector switches by way of a socalled conference number.

Referring now to Fig. 1, two automatic substations A and A v are shown having rotary line switches C and C of the usual con struction individual thereto. These line switches in common with a plurality of similar line switches have access to trunk lines terminating to local connector switches, two of these being shown terminating in conmagnet.

nectors H and H, Figs. 2 and 4. These connectors are of the Strowger type and have the usual set of 100 bank contacts arranged in ten rows or levels. On all levels the switch H has access to local subscribers lines and functions as an ordinary connector switch. On certain numbers, in this case the conference number 30, the connector H "switches through in, the same manner as a selector but at this time it does not have the trunlr selecting feature. All the bank contacts 1n the connector H are multiplied in the usual manner into all the other local connector switches, this multiple being illustrated 1n the drawings between the switches H and H. i The multiple leading from the conference number 30 terminates 1n the switch F. This is a rotary switchhaving a trunk selecting function similar to a rotary line switch besides several other features which will a pear fully later. The trunks accessible to t e lineswitches C and C are also accessible to the switch F but the trunks in themselves difi'er inasmuch as they consist of four conductors instead of three. It will be noted that the wipers of the line switches C and G are not shown associated with the same trunk line. They have not been so shown for the reason that these switches have no normal position and their wipers might be I in engagement with any trunk line.

Having briefly described the construction of the apparatus used inthe system a detailed description of its operation'will now 99 be given. For this purpose it will be assumed that the subscriber at substation A desires to hold a conference. He will therefore remove his receiver and operate his calling device for the usual local number of the first subscriber desired in the conference prefixing the conference number 30. When the receiver is removed at substation A a circuit is completed over the line conductors 11 and 12 for the line relay 16 of the line 100 switch C. Upon energizingfthe line relay 16 closes at its armature 21 a circuit which includes the switching relay 15'and the stepping magnet 17 in series, and at its armature 20 connects the test wiper 28 to the above circuit at a point midway between the switching relay and the said stepping The operation nowdepends upon whether the trunk line with which the wipers of the line switch C are associated is. or 11 test contact with which the testtwiper 28 is in engagement will be grounded, and as a result the switching relay 15 will heshort circuited and the stepping magnet 17, being supplied with direct ground by way of the test wiper' will operate as a buzzer to advance the switch wipers step by step 1n search of an idle trunk line. It may be assumed, however, that when the call is imtiated the wipers of the line switch C are standing upon the bank contacts shown 1n the drawings, and it may be assumed further that the trunk line extending from these bank contacts is idle. Under these circumstances the test contact 33 will-have no ground potential upon it and when the re-' ceiver is removed the energization. of the line relay 16 is followed immediately by the energization of the switching relay 15. Itmay bestated atthis point that the switching relay is of comparatively h gh resistance soas to prevent the operation of the stepping magnet 17 at this time. As a result of the.energization of the switching relay 15 the line conductors 11' and 12 are disconnected from the line relay 16 and from ground, respectively, and are extended by way of armatures 23 and 24 and their front contacts, wipers 27 and 29, bank conta-cts 32 and 34, conductors 53 and 55, conductors 71 and 77, normally closed springs controlled by relay 90, normally closed springs controlled by the relay-100, normally closed springs controlled by relay 101 and thence throu h the upper and lower windings of the line relay 103 of the connector H to battery and ground, respectively.

When the calling line is extended to the switch H as above described the line relay 103 is energized over the line circuit in the usual manner and completes the circuit of the slow acting release relay 104. Upon energizing, the atter relay prepares the circuits of the switch H for operation at armature 134 and at armature 132 connects ground to the release trunk conductor 73 thereby establishing a holdin circuit for the line switch C which exten s by way of' the conductor 54, test contact 33, test wiper 28, armature 25 and its front contact, winding of the switching relay 15 and the winding of the stepping magnet 17 to )battery. The above circuit 15 completed before the slow acting line relay 16 has had time to deenergize and serves to maintain the switching relay 15 energized throughout the connection. Ground is also extended by way of the private normal conductor 66 to multipl connected test contacts in the banks of t e local connector switches which have access to the line of substation A where'- by the said line is protected from intrusion in the well known manner.

The calling subscriber may now operate sent.

his calling device in accordance with the first digit of the conference number namely 3. Three interruptions are thereby produced in the line circuit of the line relay 103 which deenergizes a corresponding number'of times the series relay 106 and thence through the winding of the vertical magnet 110 to battery. The above is thecir'cuit over which the first impulse to the vertical magnet is Upon the first'vertical ste of the shaft theofl' normal springs are shifted and the circuit for the vertical'magnet is then completed over a new path which; is the same as the one previously traced except that it includes the off normal springs 156 and 158 and armature 141 and its front contact, relay 106 now being in an operated position. MagnetllO operates to raise the switch wipers 160-162, inclusive, step by step until they are placed opposite the third level of bank contacts. Relay 106 is energized in series with the vertical magnet and maintains its armature attracted throughout 'the vertical operation of the switch and at the termination of the vertical movement deenergizes and transfers the operating .cir-

cuit to the rotary ma et 111.

The calling subscriber may now operate his calling device in accordance with the last digit of the conference number'namely 0. Ten interruptions are thereby produced in the line circuit of the relay 103 which deenergizes a corresponding number of times each time sending an impulse to the rotary magnet 111 over the following circuit: Ground G, armature 129 and its back contact, armature 125 and its back contact, armature 116 and its back contact, armature 134 and its front contact, olf normal springs 156 and 158, armature 141 and its back contact, armature 148 and its back contact, winding of the slow acting series relay 107, back contact and armature 153, and thence through the winding of the rotary magnet 111 to battery. Magnet 111- operates to rotate the wipers 160-162,inclusive, into enga ement with the set of contacts associated with the conference number 30, which we will assume, are the bank contacts 165- 167, inclusive. Relay 107 is energized in series with the rotary magnet and, being a slow acting relay, maintains its armature attracted throughout the rotation of the switch, operating to connect the test wiper 161 to the test relay 108.

When the switch wipers are rotated into engagement with the conference number the spring. 120 is shifted into engagement with the spring 121 by the operation of the cam on the switch shaft. However, this operation will-have no effect at this time. The further operation of the connector H depends upon whether or not the conference number is busy. If busy, a ground potential will be present on the test contact 166 engaged by the test wiper 161. A circuit is thereby completed extending from the said grounded test contact, by way of the tett wiper 16 l, armature 143 and its front contact and through the winding of the test relay 108 to battery. Upon energizing, the relay 108 establishes a locking circuit for itself at armature 147 and at armature 149 places the busy tone from the busy machine T on the calling subscribers line. This tone will inform the subscriber at substation A that the conference number is busy at this time and he will therefore, hang up his receiver initiating the release of the switches C and H in a manner to be hereinafter described.

However, it will be assumed in the present case that the conference number was idle when connection thereto was attempted. Under these circumstances no ground will be present on test contact 166 and there will be no circuit for the test relay 108. Following the deenergization of the slow acting relay 107, a circuit is completed extending from ground on release trunk conductor 73 by way of armature 147 and its back contact, a lower winding of the switching relay 109, back contact and armature 143, test wiper 161, test contact 166, and through the resistance R to battery. Relay 109 energizes over this circuit and upon operating, establishes a locking circuit for itself at armature 152, and at armature 154 connects the lower talking conductor to the wiper 162. Another circuit completed by tlfe energization of relay 109 extends from ground on release trunk conductor 73 by way of front contact and armature 152, springs 120 and 121,

through the winding of relay 100 to battery.

Upon energizing, rela 100 disconnects the line conductors 11 an 12 of the substation A from the upper and lower windings of the line relay 103 and extends them by way of armatures 115 and 118 and their front contacts, wipers 160 and 162, bank contacts 165 and 167,-conduct0rs 186 and 188, conductor 259 which extends through the upper winding of the polarized relay 201, armature 215 and its back contact, and through the winding of the line relay 203 to battery and conductor 257 which extends by way of armature 219 and its back contact to ground.

The line relay 203 of the special rotary switch F is therefore energized over the line circuit and upon operating places ground on i the release trunk conductor 258 thereby establishing a holding circuit which extends by way of conductor 187, test contact 166,

test wiper 161, armature 151 and its front contact, front contact and armature 152 where it divides one circuit extending through the winding of the switching relay 109 to battery and the other by way of springs 120 and 121 through the winding of relay 100 to battery. This ground also extends over the release trunk conductor 73 to the line switch C. These circuits serve to maintain the switches C and H in theip operated position. Relay 203 also completes at 76 the stepping magnet 207 being supplied with direct ground by way of said test wiper operates as a buzzer to advance the switch wipiirs step by step in search of an idle trunk me. present case-that the trunk line terminating m'the bank contacts 240 to 243, inclusive,

with which the wipers of the switch F are now associated is idle and it will be assumed furthermore that the switch wipers were associated with it upon the switch being seized. Under these circumstances, following the energization of the line relay 203, the switching relay 202 is energized immediately after- However, it will be assumed in the wards. Itmay be stated at this point that the switching relay 202 is of very high re sistance so as to prevent the operation of the stepping magnet 207 at this time. By the operation of the switching relay 202 the line conductors of the calling substation are disconnected from the winding of the line relay 203 and from ground, respectively, and are extended by way of armatures 215 and 219 and their front contacts, wipers 235 and 238, bank contacts 240 and 243, trunk conductors 250 and 256, normally closed springs controlled by relay 265, normally closed springs controlled by relay 275. and then through the upper and lower windings of the line relay 278 of the connector H. Relay 278 energizes over the line circuit and completes a circuit of the slow acting release relay 279. Upon energizing, the latter relay prepares the circuits of the connector H for operation 236, armature 217 and its front contact,

through the winding of the switching relay 202, armature 212 and its back contact, back contact and armature 225 and thence through the winding of the stepping magnet 207 made and cause no difiiculty whatever in to battery. It will be understood that lease trunk conductor 258 and at the same time energizes the polarizing wlndmg of thepolarized relay 201. Before proceeding further, it will be necessary to note certain adj ustments of the relay 202 which are made to secure correct operation. The armatures 215 and 219 are adjusted to engage their front contacts before the armature 218 engages its front contact. This adjustment s made so as to prevent the energization of the The calling subscriber may now operate his calling device in accordance with the last digit of the desired subscribers number thereby producinga series of interruptions in the line relay 278 whlch deenerglzes a corresponding number of tunes 1n response thereto. At each-retraction of itsa'rmature.

307 an impulse of current is sent to the rotary magnet 294 in series with the slow acting relay 282. Magnet 294 operates to r0- tate the wipers 350-352, inclusive, into enslow acting relay 205 at this time, therelay agement with the set of contacts associated 204 energizing before it and breaklng its energizing circuit at armature 228. The p0- larized relay-201 is so adjusted that it will not attract its armatures unless current flows in the same directon in both of its windings. The necessary adjustments are all easlly practice. It will be noticed that the relay 204 is included in one side of the'line circuit and it will therefore. energize in series with the line relay 278.

. .The callin subscriber may now operate his calling evice in accordance with the first digit of the desired subscribers num-' her. A series 'ofinterruptions are thereby produced in the circuit of the line relay 278 which deenergizes in response thereto and sends a correspondingseries of impulses to the vertical magnet 295. Magnet 295 operates to raise the switch wipers 350-352, inclusive, step by step until they are placed opposite the level of bank contacts in which is located the terminals of the desired subscribers line. The slow acting rela 281 in the switch H which is energized 1n series with the vertical magnet maintains its armature attracted throughout the vertical operation of the switch and at the termination of the vertical movement deenergizes transferring the operating'circuit to the rotary magnet 294.

The operation of the various relays in the switch F in response to this digit will now be described' The relay 204 inthe switch operates in series with the line relay 278 of the selected connector and completes a circuit extending from ground G by way of armature 218 and its front contact, armature 228 and its back contact, through the winding of the slow acting relay 205 to battery.

This latter relay will now energize 1n response' to this series of impulses placing ground on the front contact of armature 229 at armature 231. An impulse of current will then be sent over a circuit extending from ground G by way of front contact and armature 231, front contact and armature 229, and thence throng-h thewinding of the slow acting relay 200 to battery. Upon energizing, this latter relay establishes a However the operation of these various relays in this switch is without function at this time and may be disregarded.

If busy, a ground potential will be present on the test contact engaged by the testwiper 351. A circuit is thereby completed from the said grounded test contact by way of the said test wiper 351, armature 322 and its front contact, and through the winding of the test relay 283 to battery. Upon energizing, rela 283 establishes a locking circuit for itse f at armature 326 and at armature 328 connects the busy tone from the "busy machine T on the lower talking conductor which extends back to the calling substation Aby way of the.- switches F, H, and C. The callings ubscriber upon hearing this tone will know that the desired subscribers line is inaccessible for the time being, and he will therefore replace his 're-' ceiver upon the switchhook thus breaking the line circuit of relay 278 which deenergizes. Upon deenergizing, relay 278 completes a circuit for the release magnet 293 of theswitch H over a path extending from ground by way of armature 307 and its back contact, armature 302 and its back contact, armature 290 and its back contact, armature-312 and its back contact, ofi' normal springs 313 and thence through the winding of the release magnet 293.to battery. Magnet 293 operates to restore the switch H to normal. When relay 278 deenergizes the relay 204 in the switch F which is included in the line circuit also deenergizes and its operation will have no eifect at this time. It

, subscribers number and as "before completes .the circuit of the slow acting relay 205.

will be noticed that the slow acting relay 200 is maintained energized over its locking circuit and holds ground on the release trunk conductor 258 preventing the release of. the switches H and C.

The calling subscriber may now do one of two things, wait and call the subscriber at the desired substation later or proceed to call the other parties desired in the conference. In the former case it will be necessary to release the connections now being held up, that is, the switches H and C. In order to do this the subscriber, having re placed his receiver to bring about the release of the connector H, as explained above,

' will simply remove his receiver and then replace it again. When the receiver is removed at substation A, the line relay 203 of the rotary switch F will energize and break the locking circuit of the relay 200 at armature 224 which relay will deenergize after a short interval removing ground from the release trunk conductor 258. However, this will have no efiect' if the calling subscriber holds the line as the relays 203 and 202 in turn replace ground thereon and the trunk selecting operation of the.rotary switch Wlll take place in' a manner hereinbefore explained. When the calling subscriber hangs up the receiver, since relay 200 is no longer locked up, this ground is removed from the release trunk conductor 258 and all the switches are restored to normal in a manner hereinafter described.

In the latter case the callin subscriber after removing his receiver will proceed to operate his calling device. in accordance with the digits of the next subscribers number.

'It is assumed that the connector H was [ill selected by the rotary switch. When the calling device is operated for the first digit of the second subscribers number the line relay 278 responds to the interruptions of its line circuit to control the operation of thevertical magnet 295. Magnet 295 operates as before to raise the switch wipers 350-352, inclusive, step by step until they are placed opposite the level of bank contacts in which the set of contacts associated with the desired second subscribers line is located. As before, the relay 204 in the switch F operates to complete the circuit of the slow acting relay 200 which energizes and establishes a locking circuit for itself at armature 211 and places ground on the release trunk conductor 258 at armature210.

The calling subscriber may now operate his calling device in accordance with the last digit of the subscribers number again producing a series of interruptions in the circuit of the line relay 278 which operates to .control the operation of the rotary magnet 294 in stepping the switch wipers into engagement with the set of bank contacts 360- .362, inclusive, associated with the line of the subscriber at substation A. As before, the slow acting relay 282 is energized in series with the rotary magnet 294. It will be assumed in the present case that the desired subscribers line is idle. Under these conditions no ground will be present on the test contact engaged by the test wiper 351 and there will be no circuit for the test relay 283., Upon the deenergization of the slow acting relay 282 a-circuit is completed extending from ground on release trunk con ductor 253 by way of the armature 326 and its back contact, lower winding of the switching relay 284, back contact and armature 322, test wiper 351, test contact 361 of the desired subscribers line engaged by the said test wiper 351 and thence over the private normal conductor 181, conductor 69, through the winding of the switching relay 43 and through the winding of the stepping magnet 45 of the line switch C associated with the line of the called subscriber at substation A to battery. v The switching relays 284 and 43 energize over this circuit. However, due to a mechanical interlocking device controlled by the armature of the line relay its front contact, wiper 352, bank contact- 362 and then over-the line circuit of the called subscriber at substation A, bank contact 360 engaged by the wiper 3.50 and the said wiper, back contact and armature 289, armature 315 and its back contact, upper winding of the ring out oif relay 280, front contact and armature 330 and through the windin of the rotary magnet 294 to battery. When the called subscriber answers the ring out off relay 280 energizes over the line circuit and completes the talking connection at the same time opening the above traced ringing circuit. It will be understood of course that the rotary magnet 294, while it I is included in the circuit of the ring cutoff relay 280, does not receive enough current to energize. The back bridge relay 276 will be energized over the line circuit of the called subscriber at substation A. and will operate at armatures 300 and 301 to reverse the battery back over the line of the calling subscriber at substation A. Upon operating, relay 276 completes a circuit of the slow acting relay 277 in an obvious manner at armature 294. Upon energizing. the latter relay establishes a locking circuit for itself gizes,

at armature 304 and at armature 303 opens the normal circuit to the line relay 278 but because of the operation of the back bridge relay 278 this circuit has already been opened and therefore this operation will have no function at this time. When the switching relay 202. The ground is placed on wiper 237 over the following circuit: Ground by way of armature 224 and its back contact, and armature 213 and its front contact. This ground extends by Way of wiper 237, bank contact 242, conductor 254, and through the winding of the slow acting relay 265 to battery. This latter relay enerestablishes a locking circuit for itself at armature 267 and at armatures 266 and 268 places the called subscriber in connection with the conference holding trunk comprising conductors 251 and 255. The line relay 278 of the switch H is ma ntained operated by the high impedance bridge 206 across the conductors of the holding trunk. Upon deenergizing, the relay 202 again completes the circuit of the linerelay 203 which ener izes over the line circuit placing ground on t c release trunk conductor 258 at armature 222. It will be noticed that. the line rela 203 at armature 224 breaks a point in the ocking circuit of relay 200; this provision is made so that upon the relay 201 deenergizing, as it will immediately following the deenergization of relay 202, the relay 200 will not again lock itself before it has deenergized. It will be understood that the line relay 203 energized before the slow acting relay 200 has had time to deenergize and thus ground is maintained on the release trunk conductor 258 and on the holding trunk conductors 57 and 252.

Upon energizing, relay 203 at armature 224 also completes a circuit which includes the switchin rela 202 and the stepping magnet 207 in series and at armature 223 connects the test wiper 236 to the above circuit at a point midway between the switching relay and the said stepping magnet. Ground will now be present on test contact 241 engaged by the test wiper 236 and the switching relay 202 will therefore be short circuited and the stepping magnet 207 being supplied with direct ground by way of the said test wiper will operate as a buzzer to advance the switch wipers step by step in search of an idle trunk line. When this is found there will be no ground present on the test contact engaged by the test wiper 236 usual manner to establish a holding lockingcircuit for the switching relay 202 of the rotary switch F.

The callin subscriber may now' operate h is calling evice' in accordance with the digits of the next desired subscribers numher. The line relay of the connector so seized will operate in response to these digits to control the operation of the vertical ma net in stepping the wipers op osite the lev l of bank contacts in which is located the contacts associated with the desired,

subscribers line. A series of interruptions is each time produced in the circuit of the series relay 204 which operates .to close the circuit of the slow acting relay 205. Relay 205 energizes and at armatures 230 and 233 opens the inductive connection to the first called subscriber thereby preventing him from receiving any of the dialled impulses sent by the calling party which would otherwise cause him some annoyance. By

the operation of the slow acting relay 205,

relay 200 is again energized the latter relay operating to .place ground on the holding and release trunk conductor at arma ture 210 and to establish a locking circuit for itself at armature 211.

When the calling device is operated for the first digit of the subscribers number the relay 204 in the rotary'switch- F and the line relay ofthe last seized connector switch are energized and deenergized in response thereto. As before, the operation of the relay 204 has no function at this time. The line relay of the connector switch how- .ever in actuating, controls the operation 01' its associated rotary magnet in rotating the switch wipers into engagement with the bank contacts associated with the line of the next subscriber desired. The slow acting relay in the seized switch similar to relay 282 energizes in series with the rotary magnet and operates to connect the test wiper to the test relay similar to 283. The

n 3 operation of the seized connector switch now depends upon whether or not the line associated with the set of bank contacts with which the wipers are inengagement is or is not busy. If busy, a ground potential will be present upon the test contact engaged by .the test wiper and the test relay will be energized. Upon energizing,

ill

the testrelay establishes a locking circuit:

for itself and places the busy tone on the line of the calling subscriber. The calling subscriber upon hearing this tone will replace his receiver upon the switchhook thereby initiating the release of its last connector switch. But the switches F, H, and C, are maintained operated as before described, also the connector H will be maintained operated because-the relay 265 has established a locking circuit for itself to ground on release or holding trunk' conductor 252 by way of armature 267. It will therefore be seen that only the connector switch last used is restored to normal and all the other connections are maintained. Thus, this provision will enable the calling subscriber to release only the. last connec- 'tion and maintain all the others.

It will now beassumed that the line of the last named desired subscriber was idle when connection was attempted therewith. Under theseconditions the switching relay similar to relay 284 in the associated connector switch will be energized and will opcrate to close the ringing circuit. Ringing current will now be intermittently applied to. the line of the called substation until the subscriber thereat responds. When this occurs a circuit will be completed for the ring cut off relay which will energize, stopping the rin ing and completing the circuit to the back ridge relay. The back bridge relay of this connector will now operate to reverse the battery-over the calling subscribers line. The polarized relay 201 in the switch F will be again energized and will operate as before described to break the locking circuit of relay 200, to open the circuit of the switching relay 202' and to energize the relay similar to relay .265 in the last operated connector switch. This latter relay will energize placinglthe second called subscriberonto the conference holding trunk comprising the conductors56 and 58 and at the same time looking itself to ground on the release or holding trunk con- (luctor, 57. The rotary switch F will then operate in the manner described hereinbefore to select another trunk line terminating in an idle connector switch.

In the same manner as above described the calling subscriber may .call the next sub scriber desired in the conference and so on.

lVhen the last connection has been established the connector used in this connection will operate to reverse the battery over the calling subscribers line thereby operating the polarized relay 201 and causing the switch F to select another idle trunk in the manner described before. The relay 201 also causes the energization of the trunk relay similar to the relay 265 thereby shifting the last subscriber into connection with. the conference holding trunk. Conversation may now take place between the calling and all 6' the called subscribers over the heavy talking conductors. 7

Should any one of the subscribers in the conference desire to retire therefrom at any time before the calling subscriber hangs up he may 'do so simply by replacing hls receiver upon the switchhook. For the purposes of description 'it'will be assumed that the subscriber at substation A desires to retire from the conference. When'the receiver is replaced at this substation back bridge relay 276 of the associated connector H will deenergize thereby restoring the normal connections of the line relay with regard to the conference holding trunkfco'nductors 251 and 255. As before mentioned, theslow acting relay 27 7 at armature 303'opens the nor- When the conference is terminated the calling subscriber at substation A will replace his receiver upon the switchhook there y causing the deenergization of the line relay in the connector switch last selected. Ground is therefore removed from the release trunk conductorthus opening the holding circuit of the switching relay 202 which deenergizes removing ground from the release trunk conductors 258, 252 and 57; The switches F, H, and C, also restore to normal in the-usual manner as there is no holding circuit for the relays 15, 100- and 109. When ground is removed from the release trunk conductors 252 and 57 the locking circuits of the trunk relays similar to relay 265v is opened and each relay I thus deenergizes. The line relays of the operated connector switches will deenergize butthe connectors will maintain their operated position until the called subscriber hangs-up as the'release ma et circuit of each operated switch is maintained opened by the associated back bridge relay similar to relay 276. During this interval before the called subscribers have hung up, ground is maintained on each of the release trunk conductors. The circuit by which this is accomplished will, be de- Having described how a conference is established between a number of subscribers the manner in which an ordinary local connection is set u Wlll now'be explained.

I For this purpose it will be assumed that the and operate his calling device in-accordance with the digits of the'number assi ed to the subscriber at substation A. W en the receiver is removed at substation A the line switch C individual thereto operates in the usual manner to-select an idle trunk line terminating in an idle connector switch. It will be assumed that the connector H was idle at this time and was selected for use;

When the calling subscriber operates his calling device for the first digit of the desired number a series of interruptions are produced in the circuit of the line relay 103 which deenergizes a corresponding number of times. A series of impulses are thereby sent over the followin path: ground G, armature 129 and its back contact, armature 125 and its back contact, armature 116 and its back contact, armature 134 and its 1 front contact, ofl normal springs 156 and 157,

winding of the series relay 106 and through the winding of the vertical magnet 110 to battery. The above is the circuit, over which the first vertical im ulse is transmitted. Upon the first vertical step of the switch the off normal springs are shifted and the remaining impulses to the vertical magnet traverse a different circuit which is the same as the one previously traced except that it includes the oil normal springs 156 and 158 and armature 141 and its front contact, the slow acting relay 106 being new in operated position. The magnet 110 opcrates to raise the wipers 160-162, inclusive, step by step until they are placed opposite the level of bank contacts in which is terminated the desired subscribers line. The slow actingv relay106 is energized in series with the vertical magnet and maintains itsarmature attracted throughout the vertical movement of the switch and at the end of the vertical operation deenergizes transferring the operating circuit of 'the connector H to the rotary magnet 111.

The calling subscriber may now operate his calling device in accordance with the last digit of his number. The line relay 103 operates in response thereto to send a corresponding number of impulses to the rotary magnet 111 in series with the slow acting relay 107. Magnet 111 operates to rotatethe switch wipers step by step until they are placed in engagement'with the set of contacts associated with the desired sub scribers line which we will assume, are the set of contacts 171-173, inclusive, associated The slow acting relay 107 is energized in series with the rotary magnet and upon operating connects the test wiper to the test relay 108. The further operation of the switch depends upon. whether or not the line of the subscriber at substation A is busy or idle. If busy a ground potential will e present on the test contact 172 and a circuit will completed for the test relay 108. Upon operating, this latter relay places the busy tone on the calling subscribers line and establishes a locking circuit for itself. The calling subscriber upon hearing this tone will replace his receiver thereby releasing the switches H and G in the usual manner.

It will be assumed, however, in the present case that the line of the subscriber at substation A was idle when the connectorH attempted to connect thereto. Under these circumstances there will be no ground potential upon the test contact 172 and the test relay 108 will not energize. Then, following the deenergization of the slow actin relay 107 a circuit is completed for the switching relay 109 extending from ground on release trunk conductor 73 by way ofarmature 147' and its back contact, lower winding of the switching relay 109, back contact and armature 143, test wiper 161,

test'contact, 172, private normal conductor the substation A from their normal battery:

and ground connections. The switching relay 109 upon energizing, establishes a locking circuit for itself at armature 152 and at armature 154 completes the ringing circuit. Ringing current is then intermittently applied to theline of the subscriber at substation A until the subs'criberthereat answers. When the receiver is removed at the called substation, the ring cut off relay 105 energizes, opens the ringing circuit, and completes the talking connection. The back bridge relay 101 energizes over the called subscribers line, operates to reverse the battery to the calling subscriber, and to complete the circuit of the slow acting relay 102 which energizes and locks. Conversation may now take place between the two subscrlbers over the heavy talking conductors. Battery being supplied to the calling subscriber from "the windings of the line relay 103 and to the called subscriber from the windings of the back bridge relay 101.

When the conversation is terminated the calling subscriber will replace his receiver upon the switchhook thereby opening the circuit of the line relay 103 which deenergizes opening the circuit of the slow acting called subscriber have replaced his receiver upon the switchhook before the calling subscriber, the back bridge relay 101 would deenergize. The circuit of the line relay is then opened at armature 124 and thereafter the connector H is released. All the foregoing operations take place in a manner full described hereinbefore.

aving fully described and ascertained the features of my invention what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim as my invention is:

1. In an automatic telephone system, means controlled by a calling subscriber for connecting with a called line, means includ-' ing a reoperative switch for then extending the connectionto a lurality of other called lines, each time maintaining the last established connection, and means whereby the subscriber on one of said called lines can disconnect his line from said connection.

2. In an automatic telephone system, means controlled by a calling subscriber for connecting with a called line, means including a reoperative switch for thenextending the connection to a plurality of other called lines, while the receiver at the calling substation is maintained off the switch-hook,

each time maintaining the last established connection, and means whereby the sub-' scriber on one of said called lines can disconnect his line from said connection.

3. In an automatic telephone system, means controlled by a calling subscriber for connecting with a called line, means including a reoperative switch for then extending the connection to a plurality of other calle lines, each time maintaining the last established connection, and means whereby the subscriber on one of said called lines can disconnect his line without disturbing the connection betwec'n the other lines.

4. In an automatic telephone system, means controlled by a calling subscriber for connecting with :1 called line, means includtion between the other lines.

each time maintaining the last established connection, and means whereby the sub-o scriber on one of said called lines candisconnect'his line without disturbing the connec- 5. In an automatic telephone system, means controlled by a calling subscriber for connecting with a called line, means including a reoperative switch for then extending the connection to a plurality of other calle lines, each time maintaining the last established connection, and means whereb the subscriber on the first called line can dlsconnect his line without disturbingthe extended connection.

6. In an automatic telephone system, means controlled by a calling subscriber for connecting with'acalled line and then extending the connection to a plurality of other called lines, each time maintaining the last established connection, and means whereby said calling subscriber may. disconnect h1s line withoutdisturbing the extended connection.

7 In a telephone system, a calling subscribers line, a holding trunk. a plurality of called subscribers lines adapted to be associated therewith, and means whereby a subscriber on said calling line may successively connect all of the said pluralit of called subscribers lines with said hol ing trunk, said means comprising a like number of automatic switches intervening between the said holding trunk and the called line in each'case.

8 In a telephone system, a calling subscribers line, a holding trunk, a plurality of called subscribers lines adapted to be associated therewith, and means whereby a subscriber on said calling line may successively connect all of the said plurality of called subscribers lines with said holding trunk while the receiver at the said calling substation is maintained off the switchhook, said 9. In a telephone system, calling and called subscribers lines, automatic switches, a trunk line terminating in each of said switches, means whereby a subscriber on one of said calling lines may-establish a connection with one of said called lines through a series of said trunk lines and automatic switches, a holding trunk, and means controlled by the response of the subscriber on the connected called line for placing his lineinto connection with said holding trunk.

10. In a telephone system, callin and called subscribers lines, automatic switches, a trunk line terminating in each of said switches, a holdingwtrunk, means whereby a subscriber on one of said calling lines may set up a plurality of connections with a number ofdsaid trunlrlines and called by way of said automatic sw tches, and means controlled by the response of the subscriber on each called line for placin the said line in connection with the said ho din trunk.

. 11. In a telephone system, ca ing 'and called sfibscribers lines, automatic switches,

a holding trunk, means. whereby the subscriber on one of said calling lines may suecessively establish a plurahty' of connections with a plurality of said called lines, said' cessively establish a plurality of connec.

tions with a plurality of said called lines, and means whereby a local connection is maintained between the said called lines by way of said holding trunk after the subscriber on the said calling line has replaced his receiver upon the switchhook;

13. In a telephone system, a calling sub-- scribers line, a holding trunk, two automatic connector switches, one of said switches accessible to the other, a called subscribers line accessible from either connector switch, means whereby the subscriber on the said calling line may establish a connec tion with the said called line directly from said first automatic switch, means-whereby the subscriber. on said calling line may es-. tablish' a second connection with the said called line by way of both connector switches,

a relay, means for energizing said relay upon the response of the subscriber on the said called linein the second connection. and means controlled by said relay for extending the said called line into connection with the said holding trunk.

14. In a telephone system, a calling subscribers line, automatic switches, a holding trunk, a plurality of called lines adapted to be associated therewith, means under the control of the subscriber on the said calling line for establishing successively a connection with each of said called lines, a relay, means for energizing said relay upon the response of thesubscriber on each of said called lines. and means controlled by said relay in each case for connecting the answering called lines together on said holding trunk. a

15. In a telephone system, a calling subscribers line, automatic switches, a holding trunk, a plurality of called lines adapted to be associated therew1th,.mean s under the control of the subscriber on the said calling line -for establishing successively aficonnection trunk in mu with each if said called lines, relays, contacts onsaid rela s connected to saidholding ltiple, and means for energizing one of said relays upon the response of the subscriber on each one of said called lines for connecting the said called lines to the holding trunk.

16. In atelephone system, a calling subscribers line, automatic switches, a olding trunk, a plurality of called lines adapted to be associated therewith, means under the control of the subscriber on said calling line for establishing successively a connection with each off said called lines, relays, means for energlzmg one'of said relays upon the response of the subscriber on each one of said called lines, means controlled b eachrelay to connect the associated called ine to the holding trunk, and means for maintaining each ofsaid relays energized to maintain the associatedcalled line'in connection with said holding trimk after the subscriber on the said calling line hangs up. w

17 In a telephonesystem, a group f connectors, an automatic hunting switch aving access to said connectors, means including said hunting. switch and one of said connectors for extending a connection to a called line, and means controlled by the res onse of the called subscriber for causing said hunting switch to select and connect with another of said connectors.

18. In a telephone system, automatic switching mechanism responsive to the dialling of a'plurality of telephone numbers in immediate succession one after the other, and

by the same calling subscriber,for connecting the stations corresponding to such numbers together, said switching mechanism comprising a group of connectors having access to the called stations, an automatic hunting switch, and circuit arrangements effective each time after a connector connects up a called station for operating said hunting switch to select another connector for use by the callingparty in -connecting up the next called station.

v 19. In a telephone system, automatic switching mechanism responsive to the dialling of a plurality of telephone numbers in immediate succession one after the other, and by the same calling subscriber, for connecting the stations corresponding to'suclv numberstogether, said switching mechanism compris ng a group of connectors having access to said called stations, an automatic hunting sw.tch, and means for operating said hunting switch between the calling of every two consecutive telephone numbers for selecting 'a different connector for use by the calling subscriber. I

'20. In a telephone system, a connector, a trunk line terminating 'in said connector, automatic switches having access to said connector over two different paths,.means for said connector and extending ,a connection to a called line, and relay means operated upon response of the subscriber on said called line only when said-connector is seized over a certain one of said paths, to complete aconnection to said called line over said trunk line. 7

21. In a telephone system, a connector, a trunk line terminating in said connector, automatic switches having access to said 'connector over two different paths, 'means for operating one of said switches for seizing said connectorand extending a connection to a called line, and relay means operated upon response of the subscriber on said called line only when said connector is seized over a certain one of said paths to complete a connection to said called line over said trunk line, said relay means being inoperative when said connector is seized over the alternative path.

22. In a telephone system, aconnector, a trunk line terminating in said connector and provided for establishing a plurality of simultaneous talking connections thereover, automatic switches, said connector being accessible to said switches over two difierent paths, means for operating one of said switches for seizing said connector and ex ing a connection to'a called line, and relay means individual to said connector and operated upon respon e of the subscriber on said called line only when said connector is seized over a certain one of said paths, to complete a connection to said called line" over said trunk line.

24. In a telephone system, a trunk line,

said trunk line terminating in a plurality of connectors and provided to serve a plurality of sin'iultaneous talking connections, certain ones of said connectors being accessible over two different paths, means for seizing one of said connectors and extending a conncction to it called line, and relay means individual to said connector and operated upon response of thesubscriber on said calledl'ne only when said connector is seized over a cer-. tam one of said paths, to complete 'a con-i nection to said called line over said trunk line, said relay means being inoperative when said connector is seized over the alternative path.

25. In a telephone system, a trunk line arranged to serve a plurality of simultaneous talking'connections, a connector switch havingaccess to called lines under numeric control of acalling line, and having access to said trunk line over a certain level, means for seizing and-for operating said connector to said level, automatic hunting means ef-- fective. wl'ien said connector is operated tosaid" le' el,, To. provide for further numeric teieetio nit called line, and relay means operatedjuponresponse of the subscriber on said called line to complete a connection to [said called line over said trunk line.

26. In a'telephone system, the method of connecting more than two subscribers in a simultaneous talking connection by means of a connector which ordinarily serves for two party connections, consisting in operating said connector to a certain level to seize a trunk line, and operating a relay ,upon the response of the subscriber on a called line to complete a connection over said trunk line. i

27. In a telephone system, the method of connecting more than two subscribers in a simultaneous talking connection by means of a connector which is accessible to automatic switches over two different paths and having a trunk line. terminating therein, consisting in operating said connector into engagement with a called line, and operating a relay upon the response .ofthe subscriber on saiil called line to complete a connection over said trunk line only when said conncctor is seized over a certain oneof said paths. V i

In a-telephone system, the method of connecting a plurality of subscribers lines in simultaneous talking relation over a trunk l ne terminating in a plurality of connector's, certain of said connectors being accessible over two different paths, consisting in operating one of said connectors to extend a connection to a called line, and operating'a relay, individual to said connector, upon response of the subscriber on said called line only -when said connector is reized over a certain one of said paths.

29'. In a telephone system, a completed connectionextending from a calling line to a called line and including a plurality of switches and trunk sections, means in one of said switches controlled from the called line for interrupting .said' connection. other switches. andmeans for re-operating said switch into engagement with one of said othcr switches for extending said calling line into connection with another called line. 30. In a telephone system, a conipletgd connection extending from a calling line to Hill a called line and-including a plurality of switches and trunk sections, means 1n one of said switches controlled from the called line for interrupting said connection, other switches, means for re-operating said switch into engagement with said-other switches to extend sa1d calling line to a plurality or called lines, successively and under control of said calling line.

32. In a telephone system, a completed connection extending from a calling line to a called line and including a plurality of switches and trunk sections, means in one of said switches controlled from the called line for interrupting said connection, other switches, means for re-operating said switch into engagement with said other switches to extend said calling line to a plurality of called lines, successively and under control of said calling line without releasing said first called line;

33. In a telephone system, a completed connection extending from a calling line to a called line and including a plurality of switches and trunk sections, means in one of said switches controlled from the called line for interrupting saidconnection, other switches, means for re-operating said switch into engagement with said other switches to extend said calling line to a plurality of called lines successively of said calling line without releasing said first called line, and means for connecting said calling line into talking relation with said called lines.

34. In a telephone system, a completed connection extending from a calling line to :1 called line and including a plurality of switches and trunk sections, means in one of said switches controlled from the called line for interrupting said connection, other switches, means for re-operating said switch into engagement with said other switches to extend said calling line to a plurality of called lines successively and under control of said calling li'ne without releasing said first called-line, and means for connecting said calling line in'talking relation with said called lines aftersaid callingnline-has established connection with the last called line.

35. In a telephone system, a calling line, afirst called line, a plurality of trunk sections' and switches controlled from said calling line successively to extend a connection and under controlto said first called line, other'called lines accessible from one of said switches, means in I said switch controlled from said first called line for interrupting said connection, and

switching 'means co-operating with said switch to extend said calling line into con- .nection with other called lines under control of said calling line.

36. In a telephone system, a calling line, a first called line, a plurality of trunk sectionsand switches controlled from said callmg lme successively to extend a connection Ten 7 to said first called line, other called lines accessible from one of said switches, means in sa1d switch controlled from said first called line for interrupting said connection,

and switching means controlled by said callmg line and co-operatingiwith said switch to extend said calling line into connection with other called lines without releasing said first called line.

37. In a telephone system, a callin line, a first called line, a plurality of tru seclions and switches controlled from said callmg line successively to extend a connection to said first called line, other'called lines accessible from an intermediate one of said switches, means in said switch controlled from said'first called line for interru ting said connection, and means controlled by said calling line and co-o crating with said switch for extending sai calling line into connection with a plurality of other called lines without releasing said first called line, said switch being provided with means to establish talking connection with said first called line when said calling line has completed the connection to the last called line.

38. In a telephone system, the method of connecting a plurality of lines into simultaneous talking relation, consisting in the operation of an automatic switch which is included in a train of switches connecting a calling line with a called line, and the operation of a relay controlled from the called line to interrupt said train at said switch and to cause said switch to establish connection with a plurality of other called lines under control of the calling line. 7

39. In a telephone system, the method of connecting a plurality of lines into simultaneous talking relation, consisting in the operation of an automatic switch which is included in a train of switches connecting a calling line with a called line, and the operation of a relay controlled from the called line to interrupt said train at said switch and to cause said switch toestablish connection with other called lines. under control of the calling line without releasing the called line.

Signed by me at Chicago, Illinois, this 20tl1'.day of January 1921.

i 7 JOHN E. GARDNER. 

